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Laser welding of dissimilar metals (steel and aluminium) was investigated with the aim to increase the maximum tensile shear load of the Fe-Al joints. The increase was achieved by texturing the surface of steel prior to the laser spot welding process which was performed in a lap-joint configuration with the steel positioned on top of the aluminium and with a texture faced down to the aluminium surface. This configuration enabled an increase of the bonding area of the joints, because the molten aluminium filled in the gaps of the texture, without the need of increasing the process energy which typically leads to the growth of the intermetallic compounds. Different textures (containing hexagonally arranged craters, parallel lines, grid and spiral patterns) were tested with different laser welding parameters. The Fe-Al joints obtained with the textured steel were found to have up to 25% higher maximum tensile-shear load than the joints obtained with the untextured steel.

The integrity of steel-aluminium dissimilar alloy joints is dependent on the thermal cycle applied during the joining process. The thermal field has a direct influence on the growth of the intermetallic compounds (IMC), which result from the reaction between iron (Fe) and aluminium (Al), but it also determines the size of the bonding area of the joint. A finite element (FE) thermal model was developed to predict the transient thermal cycle at the Fe-Al interface for different levels of applied energy by changing the power density and interaction time. The time-temperature profiles were correlated to the weld geometry, IMC layer thickness and mechanical strength. The experimental results showed that having a small bonding area is equally detrimental to the mechanical strength of the joint as having a thick IMC layer. The FE model suggested that comparing to time, the temperature is more important in laser welding of steel to aluminium as this is the factor which most contributes to the growth of the IMC layer and the formation of the bonding area. However, it was not possible to identify a thermal field able to produce simultaneously a large bonding area and a thin IMC layer to optimize the joint strength.

This paper investigates a resistance spot welded reinforced adhesive (weld-bonded) joint between 304 stainless steel to carbon fibre reinforced plastic (CFRP), where welds are made both with and without the reinforcing carbon fibres present. Successful welds with the fibres present could only be produced with high electrode pinch forces, which helped reduce contamination of the weld nugget. Similar joint strengths were achieved in both cases, however the joints without fibres exhibited an increased strain to failure. Both joints were significantly stronger than either an adhesive joint or a comparable bolt reinforced adhesive joint. These techniques provide an alternative for joining thin metallic components to CFRP structures where increased strength and integrity is required.

In laser welding and other processes, such as cladding and additive manufacturing, the weld bead geometry (depth of penetration and weld width) can be controlled with different parameters. A common practice is to develop process parameters for a particular application based on an engineering approach using the system parameters i.e. laser power and travel speed. However, in such a case the process is optimised for a particular system only. This study is focused on understanding of the phenomena controlling the weld profile in conduction welding for a wide range of beam diameters from 0.07 mm to 5.50 mm. It has been shown that the weld bead geometry can be controlled by the spatial and temporal distribution of laser energy on the surface of workpiece, such as power density, interaction time and energy density. This means that similar depths of penetration can be achieved with various optical set-ups. It has been also found that it is more difficult to achieve pure conduction welds with small beam diameters, which are typically used in powder bed additive manufacturing, due to high conduction losses and low vaporisation threshold.

This paper presents fatigue crack growth behaviour in titanium alloy Ti-6Al-4V built by the Wire + Arc Additive Manufacture (WAAM®) process. Process induced residual stress and stress relief by cold working were measured by neutron diffraction and contour methods. Residual stress retained in the compact tension test specimens was evaluated by the finite element method based on the measured stresses in the WAAM wall. Fatigue crack growth rate in as-built and stress relieved conditions are discussed with respect of the effects of material build orientation, residual stress, and microstructure characteristics. Key conclusions are: (a) residual stresses arising from the WAAM process can be controlled and reduced significantly by cold working. Residual stress retained in compact tension specimens is low, resulting in low residual stress intensity factor. (b) Microstructure affects fatigue crack growth rate in twodifferent material’s build orientations. (c) Fatigue crack growth rate in WAAM Ti-6Al-4V is lower than that in traditional wrought plate, with and without the residual stress relief. Therefore, WAAM is a viable additive manufacture process to produce aerospace titanium alloys for damage tolerance design.

This paper presents an experimental investigation of the fracture and fatigue crack growth properties of Ti-6Al-4V produced by the Wire + Arc Additive Manufacture (WAAM) process. First, fracture toughness was measured for two different orientations with respect to the build direction; the effect of wire oxygen content and build strategy were also evaluated in the light of microstructure examination. Second, fatigue crack growth rates were measured for fully additive manufactured samples, as well as for samples containing an interface between WAAM and wrought materials. The latter category covers five different scenarios of crack location and orientation with respect to the interface. Fatigue crack growth rates are compared with that of the wrought or WAAM alone conditions. Crack growth trajectory of these tests is discussed in relation to the microstructure characteristics

It is desirable to utilise a robotic approach in additive manufacturing as Computer Numerical Control (CNC) is expensive and it has high maintenance costs. A robotic approach is relatively inexpensive compared to CNC and can provide much more flexibility, enabling a variety of configurations and easier parallel processing. However, robots struggle to achieve high positioning accuracy and are more prone to disturbances from the process forces. This paper attempts to characterise the robot position and velocity errors, which depend on the build strategy deployed, using a laser speckle correlation sensor to measure the robotic motion. An assessment has been done as to whether these errors would cause any problem in additive manufacturing techniques, where the test parts were built using the Wire+Arc Additive Manufacture (WAAM) technique. Finally, different compensation strategies are discussed to counter the robotic errors and a reduction of 3 mm in top surface profile irregularity by varying the wire feed speed (WFS) during the path has been demonstrated.

Wire + arc additive manufacturing components contain significant residual stresses, which manifest in distortion. High-pressure rolling was applied to each layer of a linear Ti–6Al–4V wire + arc additive manufacturing component in between deposition passes. In rolled specimens, out-of-plane distortion was more than halved; a change in the deposits' geometry due to plastic deformation was observed and process repeatability was increased. The Contour method of residual stresses measurements showed that although the specimens still exhibited tensile stresses (up to 500 MPa), their magnitude was reduced by 60%, particularly at the interface between deposit and substrate. The results were validated with neutron diffraction measurements, which were in good agreement away from the baseplate.

Depositing large components (>10 kg) in titanium, aluminium, steel and other metals is possible using Wire + Arc Additive Manufacturing. This technology adopts arc welding tools and wire as feedstock for additive manufacturing purposes. High deposition rates, low material and equipment costs, and good structural integrity make Wire+Arc Additive Manufacturing a suitable candidate for replacing the current method of manufacturing from solid billets or large forgings, especially with regards to low and medium complexity parts. A variety of components have been successfully manufactured with this process, including Ti–6Al–4V spars and landing gear assemblies, aluminium wing ribs, steel wind tunnel models and cones. Strategies on how to manage residual stress, improve mechanical properties and eliminate defects such as porosity are suggested. Finally, the benefits of non-destructive testing, online monitoring and in situ machining are discussed.

Mechanical property anisotropy is one of the issues that are limiting the industrial adoption of additive manufacturing (AM) Ti-6Al-4V components. To improve the deposits’ microstructure, the effect of high-pressure interpass rolling was evaluated, and a flat and a profiled roller were compared. The microstructure was changed from large columnar prior beta grains that traversed the component to equiaxed grains that were between 56 and 139 μm in size. The repetitive variation in Widmanstätten alpha lamellae size was retained; however, with rolling, the overall size was reduced. A “fundamental study” was used to gain insight into the microstructural changes that occurred due to the combination of deformation and deposition. High-pressure interpass rolling can overcome many of the shortcomings of AM, potentially aiding industrial implementation of the process. EPSRC, AirBus

This paper reports on the design and implementation of a wireless sensor communication system with a low power consumption that allows it to be integrated with the energy harvesting technology. The system design and implementation focus on reducing the power consumption at three levels: hardware, software and data transmission. The reduction in power consumption, at hardware level in particular, is mainly achieved through the introduction of an energy-aware interface (EAI) that ensures a smart inter-correlated management of the energy flow. The resulted system satisfies the requirements of a wireless sensor structure that possesses the energy autonomous capability.

This paper presents the performance testing results of a wireless sensor communication system with low power consumption integrated with a vibration energy harvesting power source. The experiments focus on the system’s capability to perform continuous monitoring and to wirelessly transmit the data acquired from the sensors to a user base station, completely battery-free. Energy harvesting technologies together with system design optimisation for power consumption minimisation ensure the system’s energy autonomous capability demonstrated in this paper by presenting the promising testing results achieved following its integration with Structural Health Monitoring (SHM) and Body Area Network (BAN) applications.

Conduction laser welding opens up a range of innovative applications for laser welding. This relatively novel mode of laser processing expands the application potential significantly beyond what is normally achieved today. The main reason for this could be attributed to the different characteristics of conduction process when compared to keyhole laser welding. An example is the higher stability of conduction which results in welds of higher quality and better control of the welding process. Despite the advantages of conduction laser welding, it is yet to be exploited significantly for industrial applications and there are very few applications for which this mode of operation is used. This paper is aimed at presenting different varieties of applications for conduction laser welding using a fibre laser. This ranges from high quality aluminium welds to laser brazing of stainless steel to metal foams. The objective of this paper is to highlight the main features of conduction laser welding process and exemplify some conduction laser welding applications.